Mono Icons
Heroicons
Teenyicons — Tiny minimal 1px icons
Feather – Simply beautiful open source icons
Tabler icons
Lordicon Animated Interactive Web Icons
Introducing Duotone
Download free icons, music, stock photos, vectors
Font Kiko - Free Icon Font, SVG, AI, EPS - Download Now!
A complete guide to iconography
Material Icons Library
Google Play icon design specifications
Ikonate – fully customisable & accessible vector icons
iconoteka
N. Mockups
ICONSVG - Quick customizable SVG icons
Unicons
Sets - Privacy & Security
Eva Icons - beautifully crafted Open Source UI icons for common actions and items.
Better Icon Design in 6 Easy Steps – The Iconfinder Blog
http://www.evericons.com/
Boxicons
Icons - UWP app developer
My Mac app icon design workflow
Smashicons - Iconfinder.com
Iconjar & Sketch Vector OS X Cursors